Cook the pasta following the pack instructions and set to one side. Heat 1 tbsp olive oil and 2 of the garlic cloves in a pan, then stir in the chopped aubergines and onion. Cook on a medium hob for 30 minutes until softened and golden, then remove from the heat and leave to cool for a few minutes. Blitz the aubergine mixture in a food processor with the lemon juice, zest, breadcrumbs and a small handful of roughly chopped basil leaves. Shape into 25 meatballs, about 4cm in size, then set to one side on a sheet of baking parchment.
In a small saucepan, soften the remaining garlic and chilli in 1 tbsp olive oil. Stir in the tomatoes, olives, capers and sugar; season, then simmer on a medium heat for 15 minutes.
Heat the oven to 220°C/200°C fan/gas mark 7. Fry the aubergine balls in 1 tbsp olive oil until brown all over, then set aside until cool enough to touch. Spoon two thirds of the tomato sauce over the base of a large, shallow baking dish. Drop the meatballs into the cooked conchiglioni shells, then arrange on top of the cooked tomato. Spoon over the remaining sauce, then top with the torn mozzarella. Bake for 30 minutes or until golden brown. Serve with grated parmesan and basil leaves.